Download Day 2

Unit: Chemical
Reactions
Balancing chemical equations
After today you will be able to…
• Explain the Law of Conservation of
Atoms
• Balance equations using the “tally
method”
Law of Conservation of Atoms:
There must be the same
number of each type of atom
before the reaction as after
the reaction.
Coefficients: Are numbers
that go in front of each
substance to indicate the
number of atoms or molecules
that are reacting or being
produced.
 Let’s try some
examples! 
We will be using the “tally
method” to balance equations
in this class.
Examples: Balance the following equation:
2 Al + ___S
3
___
 ___Al2S3
2 1 Al 2
3 1 S 3
If the numbers match on
either side… You’re balanced!
Examples: Balance the following equation:
42 Li + ___O  ___Li
2
___
2
2O
4 2 1 Li 2 4
2 O 1 2
Examples: Balance the following equation:
3
2
2
___Fe2(SO4)3 + ___Na
3(PO4)  ___Fe(PO4) + ___Na2(SO4)
2 Fe 1 2
3 (SO4) 1 3
6 3 Na 2 6
2 1 (PO4) 1 2
Helpful tip:
Do not separate
Are
we
balanced?
YES!!!!
polyatomic ions!
Do now: Complete
“Exit Ticket”
Then: Begin WS 2
(Homework)